This project is designed to study the influence of a one-year program of progressive physical conditioning upon plasma high-density lipoproteins, other lipoproteins and upon various other risk factors for cardiovascular disease in a group of 65 initially sedentary men aged 30-55. A further 35 such men will act as a sedentary control group, and assignment to excercise or control will be random. Conditioning will be by a supervised, progressive, individualized program of walking, jogging and running. Evaluation of the participants (exercisers and controls) will be at baseline, at five points during the 1-year program, at the end of the program and finally 6 months after the program is completed. Detailed examination of plasma lipid, lipoprotein and apo-lipoprotein concentrations will be made using ultracentrifugal procedures. The activity of the plasma enzymes lecithin-cholesterol acyltransferase (LCAT) and post-heparin lipases will be determined. In this way we hope to clarify the sequence of events by which exercise leads to the characteristic (and apparently beneficial) plasma lipoprotein pattern exhibited by very active people. Serial measurements will also be made of a number of other physiological parameters reflecting the physical fitness level of the participants, or thought likely to change during excercise, including a graded exercise electrocardiogram with maximal oxygen uptake, echocardiography, resting and exercise blood pressures, weight and percent body fat (by hydrostatic weighing). Dietary intake will not be controlled but will be carefully monitored by computerized analysis of 3-day food records. Smoking habit changes (in initial smokers) will be followed by questionnaire and plasma thiocyanate measurements. Psychological changes and sleep pattern changes will be monitored by standard questionnaires.